Hm, that's interesting. My understanding was that Piapro should match up with the tempo set in your DAW. Though I'm not sure what happens if you change it inside Piapro and leave the DAW alone; it might be out of sync then.
I've often wished you could see the notes from Piapro in the DAW, too. Right now, you can get some guidance from the beat measurements at the top of Piapro/the DAW. In Piapro and Studio One (and I'm sure in any other DAW), there should be something along the top or bottom like the "ruler" you see in word processing programs--it will lay out a count of the measures and beats moving forward in time. I can see it in your screenshot--it's the 1 3 5 7 9 11 line just above your 1LDK track. As long as Piapro and your DAW are set to the same tempo, those rulers should correspond between the two programs--so when you're at measure 1, beat 1 in Piapro, you'll be at measure 1, beat 1 in your DAW. Your view is zoomed out pretty far in your screenshot and looks like it shows a number corresponding to every other measure; if you zoom in, it will show the beats within the measures, too. It's not an ideal way to line things up, but it kind of works.
that change happens when you load a VSQX or MIDI into Piapro. The tempo in Piapro will change, but Studio One will not.
In normal circumstances though, the two change together
As for matching things up, this suggestion is the best. My recommendation for how to do it though, when your Studio One and Piapro are at the same tempo, you can use the bars to estimate. I recommend playing the instrumental until the song should start, then pausing it, next to your play/stop/skip back/skip forward contrals on the left should be a time with the word bars under it (can also say seconds, frames, etc depending what you have it set to but it’s a simple click and change. )
Get that number and go to Piapro, where the numbers are along the top in a number line or ruler, as mobius compared it to. Though not as detailed as Studio One’s measure lines, you can pretty easily find where the start needs to go and just fine tune the placement with guesswork
The reason why Piapro Studio gets no track in Studio One is because the “track” is actually a part, just like in Vocaloid, a track is empty until you place a part there, but Piapro is a completely external VSTi so drawing a part does nothing for you. All external VSTis I have used, included V5, act this way.
Another thing you can do, if you are completely done with your tuning is go to Song > Export Stems which will creatr a wav of each instrument track in Studio One and you can place is in there instead of having Piapro Studio open. Keep in mind if you want harmonies in a seperate wav, you have to go to Piapro abd mute what you don’t want rendered because all of Piapro is one instrument track